1. Field of the Invention
The present invention relates to a method for producing a cholesteric liquid crystal color filter and, more specifically, to a method for producing a cholesteric liquid crystal color filter having excellent color pixel resolution.
2. Description of the Related Art
A cholesteric liquid crystal color filter can be produced by various methods. For instance, there has been proposed a method of forming an alignment layer made of polyvinyl alcohol, polyimide, etc., on a substrate, and forming a liquid crystal layer of a first color region on the formed alignment layer using a liquid crystal composition containing a liquid crystal compound, a photoreactive chiral dopant, a polymerization initiator, etc. Then, ultraviolet radiation is applied under each of predetermined temperature conditions to form regions for each of colors, and ultraviolet radiation is applied through a mask to the entire surface under a predetermined temperature condition to polymerize and fix the aligned states to establish color patterning.
Another method features forming an alignment layer made of polyvinyl alcohol, polyimide, etc., on a substrate, and forming a liquid crystal layer of one color on the formed alignment layer using a liquid crystal composition containing a liquid crystal compound, a photoreactive chiral dopant, a polymerization initiator, etc. Then, after changing pitch of liquid crystals in accordance with a quantity of applied light, this aligned state is polymerized and fixed to establish color patterning. However, liquid crystal color filters implemented by these methods are insufficient and there is still room for improvement in color pixel resolution.
The present inventors have conducted intensive researches to improve color pixel resolution, and found that one of the reasons low color resolutions were produced was molecular diffusion of the photoreactive chiral dopant, which had been isomerized by patterning exposure, in the planar direction of the liquid crystal layer during the step of aligning the liquid crystals.
In order to cope with the aforementioned problems, there have been proposed methods to improve the color pixel resolution by reducing the diffusion of the isomerized chiral dopants, for instance, by means such as (1) lowering an aligning temperature (from higher temperatures in a range of from 100 to 130° C. to about 70° C.); (2) accelerating polymerization of the liquid crystal compound in the aligned state; (3) providing photoreactive chiral dopants with higher molecular weights; etc.
However, each of the above means is insufficient, in that the diffusion of the chiral dopants isomerized by UV irradiation can only be retarded, and cannot be completely prevented.